In a gas fireplace, a combustible gas, e.g., natural gas or propane, is mixed with a source of oxygen, e.g., air, and burned. In a ventless gas fireplace, air is drawn into the combustion chamber or firebox of the fireplace typically from the room in which the fireplace is situated, and hot exhaust gases containing combustion products including carbon monoxide, carbon dioxide, nitrogen dioxide and water are vented directly into the room.
In gas fireplaces, it is desirable to adjust the air/gas ratio to create a bright yellow flame which mimics the flame produced in a wood burning fireplace. Such a flame, however, tends to produce an undesirably high level of emission products. This is particularly troublesome in a ventless fireplace which has strict emission requirements. For example, the ANSI standard for carbon monoxide emission is no more than 200 ppm. The ANSI standard for nitrogen dioxide is no more than 20 ppm. To control these emissions, an operator typically uses a clean burning blue flame, sacrificing the more aesthetically pleasing yellow flame.
Another problem associated with the use of a ventless fireplace is the generation of too much water vapor which is vented directly into a room. This not only creates high humidity, but if the fireplace is used frequently, there is a possibility of moisture condensation on the walls or other objects within the room. Yet another problem associated with ventless fireplaces is the generation of too much heat.
One method for controlling the amount of carbon monoxide and nitrogen dioxide in the exhaust of a ventless fireplace is through the use of a catalytic converter. Such a use is described in U.S. patent application Ser. No. 08/509,426 and patent application entitled "GAS FIREPLACE", filed Oct. 1, 1996, naming French, et al. as inventors. While this method is useful in controlling carbon monoxide and nitrogen dioxide levels in the exhaust, it does nothing to control the amount of moisture in the exhaust or the amount of heat generated by the fireplace. Currently, the only way to control the amount of heat and moisture generated by a ventless fireplace and vented into a room is to reduce the amount of combustion, i.e., reduce the size or quality of the flame or shut off the fireplace. Reduction or elimination of the flame diminishes the aesthetic look and appeal for which the fireplace was designed.
There is therefore, a need for a means by which an operator can control the amount of heat and moisture vented into a room by a ventless gas fireplace.